Storage tank construction



March 24, 1953 E. B. AYERS 2,632,456

STORAGE TANK CONSTRUCTION Filed Jan. 15, 1949 y a :3 v l...

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Wigwam Patented Mar. 24, 1953 STORAGE TANK CONSTRUCTION Ellsworth B. Ayers, Atlanta, Ga., assignor to Standard Oil Development Company, a corporation of Delaware Application January 13, 1949, Serial No. 70,743

3 Claims.

The present invention relates to the construction of storage tanks. More particularly, the in-- vention relates to a storage tank structure pro- Vldlllg means for substantially complete removal of the tank contents. The invention also relates to a tank structure in which the generation of static electric charges during removal of the con.- tents' is considerably minimized. It is an object of the invention to provide a means for withdrawal of the contents of a storage tank such that the liquid remaining in the tank will be of such small volume with reference to the total capacity of the tank that such quantitie of liquid as may remain after the tank has been substantially emptied willbe insufficient to cause contamination where the tank is subsequently refilled with a liquid of different character. For example, Where a tank containing a gasoline of low octane rating is emptied and refilled with a gasoline of high octane rating, the quantity of low octane gasoline which may remain in the tank will be so small as to produce no detectable change in the octane rating of the gasoline with which the tank is refilled. It is also an object of the invention to permit the withdrawal of explosively inflammable liquids in such fashion as to prevent the generation of static electric charges which may be created by uncontrolled flow of the tank contents over the tank bottom during the last stages of evacuation, or otherwise, as a result of uncontrolled agitation of th liquid contents of the tank during such final stages.

The invention and its objects may be fully understood from the following specification when read in conjunction with the accompanying drawings, in which Figure 1 is a vertical section through a portion of a tank bottom constructed in accordance with the invention, and

Figure 2 is a perspective View, partly in section, of a swirl eliminator for a tank draw-off suction line.

In the embodiment of the invention illustrated by the drawings, the numeral I designates the vertical wall of a storage tank and the numeral 2 the bottom wall thereof. In the bottom wall of the tank is provided a sump 3 which may be disposed concentrically with the tank or eccentrically thereof, as desired. This sump is formed by excavating a pit 4, below the surface level of the ground on which the tank bottom 2 is or will be supported. The pit 4 is excavated to a dimension somewhat larger than the desired finished size of the sump 3, the wall preferably being sloped upwardly and outwardly from the bottom. The

sump itself is formed by means of a hollow, frusto-conical metallic liner member 5 inserted in an inverted position substantially concentric with the pit, the smaller opening in the member 5 being provided with a closure plate 6 secured to the frusto-conical member as by welding. The outer edges of the plate 6 preferably extend somewhat beyond the edges of the opening in the member 5. The compartment formed by the liner member 5 and the closure plate 6 i then partially filled with a ballast material such as concrete, as indicated by the numeral 1. The ballast material may be any suitable material having a fairly high weight per unit volume. Although concrete is the preferred material, other materials such as sand, crushed stone, and the like may be used. The compartment is filled with such a material to a depth such that the upper level thereof is substantially coincident with the level desired for the floor of the sump, and as required to offset the buoyancy effect of the displacement volume thereof. Where the concrete ballast material is used, the surface is grouted to a substantially level condition and a sump bottom plate 8 laid over the upper surface of the ballast and welded to the sloping wall of the liner 5. Where other materials than concrete are used as ballast, it is preferable that a substantially smooth and level surface be formed either with the material itself, or by a surface layer of cement or concrete. With the sump structure 3 located substantially concentrically in the pit 4, the annular space between the sump and pit walls is filled with concrete, as indicated by the numeral 411. The bottom of the tank 2 is then joined to the upper or base edge portion of the frusto-conical member 5 in such fashion as to provide a substantially continuous, smoothly curved surface between said portion and the tank bottom.

In forming the frusto-conical member 5, it is desirable that the angle between the bottom plate 8, and the inner surface of the member 5 be not substantially less than 120, and that the angular relation between the member 5 and the bottom of the tank be not substantially more than with the curvature of the sump lip formed at the juncture between the member 5 and the tank bottom 2 being such as to provide for unimpeded flow of liquid over the tank bottom, and into the sump. In providing a smoothly curved or rounded hp at the upper edge of the sump, as well as a sloped wall for the sump, the free fall of liquid into the sump is prevented. Also, by restricting the angular relationship between the wall and bottom of the sump, as well as by restriction of the slope of the tank bottom, liquid" in the tank may be prevented from flowing over such conducting surfaces at a rate exceeding three feet per second, thereby minimizing or eliminating the generation of static electric currents.

The diameter of the sump at its upper edge is preferably governed by the maximum rate at which the contents of the tank are to be withdrawn. Preferably, the diameter, and hence the capacity of the sump, is calculated to allow a two minute time interval for substantial evacuation of the sump to within about one foot of the plate 8.

The customary draw-off line 9 is provided for pumping out the tank. This line is extended downwardly into the sump as by portion 9a, having an inlet 91). The inlet 9b is provided with a swirl eliminator which, as shown in Figure 2, is composed of an annular plate element [0, having a central opening Illa, fitted to the pipe draw-off section 90!. at inlet 9b. The inlet portion 9b extends through the central opening Illa in plate l into spaced relation to the sump bottom plate 8. From the under-surface of the plate l0 depend a plurality of baffies or swirl plate elements ll extending radially from the opening Illa to the periphery of the plate It], and spaced arcuately one from another. The bafiles ll extend from the under-surface of the plate I0 into supporting contact with the sump plate 8. If desired, the bafiles I I may be provided with shoulder-like portions Ila projecting inwardly from their inner end edges, and providing a supporting rest for the lower end of the inlet portion 912. By provision of the plate and baffles, the tank liquid being withdrawn is prevented from swirling, and forming a vortex at the inlet, thus further preventing the generation of static electric currents, and preventing loss of suction by admission of air or vapor into the pumps.

To facilitate collection and withdrawal of water and other extraneous liquids or sediment from the tank, a supplementary sump l2 may be provided in the main sump 3, preferably in close proximity to the draw-off inlet 91). Draw-off lines such as I3 and I l may be provided as required to drain the contents of sump [2.

The embodiment of the invention as described in the foregoing specification and shown in the permit substantially complete withdrawal of the liquid contents thereof, and minimize frictional generation of static electric charges therein, comprising a tank bottom, a sump in said bottom, the tank bottom being inclined uniformly toward said sump, a flat bottom plate in said sump, an inverted frusto-conical sump wall portion extending upwardly and outwardly from said bottom plate toward the tank bottom surrounding the sump, an upper bottom plate, forming the true bottom of the sump, joined-peripherally to the frusto-conical sump wall portion in vertically spaced, substantially parallel relation to said lower plate, and a body of a ballast material completely filling the space between upper and lower sump bottom plates, a smoothly curved, outwardly flared annular lip at the outer edge of said sump wall joining the sump wall and tank bottom in unitary relation, a draw-01f conduit having an inlet, extended downwardly into the sump, into spaced relation to the bottom thereof, an annular shield plate encircling the conduit, afiixed thereto adjacent the inlet, and a plurality of radially extended swirl plate elements dependent from said shield plate, around the inlet, extending into supporting contact with the sump bottom.

2. Apparatus according to claim 1, in which the frusto-conical wall portion of said sump extends upwardly and outwardly from the sump bottom at an angle not substantially less than about 3. Apparatus according to claim 1 in which the body of ballast material is a body of a cementitious material.

ELLSWORTH B. AYERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 841,176 Powers Jan. 15, 1907 969,997 Theim Sept. 13, 1910 1,493,843 Conrader May 13, 1924 1,497,425 Ames June 10, 1924 1,548,400 Walker Aug. 4, 1925 1,608,224 Mauran Nov. 23, 1926 2,165,889 Fischer July 11, 1939 2,174,354 Shields Sept. 26, 1939 2,307,616 Booth Jan. '5, 1943 2,410,338 Craine Oct. 29, 1946 2,506,927 Kelley May 9, 1950 

